The present invention relates generally to the field of piezoelectric devices, and more particularly, but not by way of limitation, to a piezoelectric actuator suitable for being mounted on the base plate or the load beam of a disk drive suspension and also to a head gimbal assembly (HGA) using the same piezoelectric actuator.
Magnetic hard disk drive technology continues to advance at a remarkable rate. Bite density has been increased significantly by using advanced head and media technology, whereas the track density still remains at a relatively lower level. To attain higher track densities, extremely accurate track following is required. This can be achieved by both reducing mechanical disturbances and by increasing the servo control bandwidth. The amount of disturbance attenuation achieved by servo systems is proportional to the square of the closed-loop bandwidth. The closed loop bandwidth of a present-day single-stage positioning system with a voice coil motor as the actuator is typically limited to around 1 kHz by the mechanical dynamics of the head stack assembly (HSA). Its capability to compensate the positioning error is roughly limited to 1 micrometer TMR. It is anticipated that several kHz""s closed-loop bandwidth will be required to attain the projected track densities, i.e., 25 kTPI, 0.1 micrometer TMR. Dual-stage actuator systems have been proposed as a reasonable solution for attaining such a wide servo-bandwidth. The dual-stage actuator system comprises a conventional voice coil motor as the primary actuator for track seeking, coupled with a secondary micro-actuator for settling and track following.
The structure, performance and mounting location of the secondary actuator are key factors affecting the overall characteristic of the dual-stage servo system. Various micro-actuators, including piezoelectric, electromagnetic and electrostatic actuators, have been developed to meet this purpose. The devices are designed to be mounted at various locations on an E-block suspension and between the suspension and slider. Taking the inertia of the entire actuator mechanism into consideration, the mounting place of the secondary stage actuator should be as close to the magnetic head as possible. On the other hand, the driving electric/magnetic field of the actuator should not affect the read/write performance of the magnetic head. From this point of view, the optimum location of the secondary actuator will be on the suspension.
One such suspension with piezoelectric actuators is disclosed in U.S. patent application Ser. No. 228,341 (U.S. Pat. No. 6,046,888) filed Jan. 11, 1999 by Todd A. Krinke et. al. entitled Base Plate-mounted Microactuator for a Suspension which is assigned to Hutchinson Technology Incorporated.
However, because of the difference between the current technology and the specifications of the industrial field, such as higher driving voltage, lower mechanical resonance frequency, not enough stroke and so on, there is a continuing need for improved suspensions with micro actuators. Actually, to meet the requirements of the industrial field, the secondary actuator must have at least xc2x11.3 xcexcm actuation stroke and the mechanical resonance frequency of the whole two-stage actuator system must exceed 13 kHz. In the present invention a piezoelectric microactuator together with the corresponding suspension and head gimbal assembly are proposed to attain the above specifications simultaneously.
A general object of the present invention is to provide new configurations for a head gimbal assembly (HGA) with a piezoelectric micro actuator, which is capable of quickly and accurately positioning the read/write head for a dual-stage head positioning actuator system of a high-density hard disk drive.
A specific object of the present invention is to provide a planar piezoelectric device, which in a preferred embodiment, can have a relatively small height or thickness, and a relatively large width and length, and can be a part of the suspension to drive the distal end of the suspension, i.e., the slider, moving across data tracks so as to obtain a two stage head positioning servo system with a high servo bandwidth.
Another specific object of the present invention is to provide a head suspension with a stationary proximal end and a moveable distal end, on which, in a preferred embodiment, a piezoelectric actuator of the present invention can be easily mounted to connect the stationary and moveable ends and to drive the distal end of the suspension, i.e., the slider moving across data tracks so as to obtain a two stage head positioning servo system with a high servo bandwidth.
Yet another specific object of the present invention is to provide an electrical connection scheme of driving voltage which can avoid depoling of the piezoelectric actuator so as to attain a large stroke by increasing the driving voltage.
In accordance with one aspect of the present invention, a piezoelectric device comprising an integral body of piezoelectric material which is longer and wider than its thickness is presented. The device is characterised in that it further includes, in contact with the body, respective pairs of electrodes, in that the electrodes of each pair are opposed in the thickness direction, in that the pairs are spaced in a direction transverse to the thickness direction, and in that the integral body is divided into two or more symmetric parts by splitting the electrodes. The body of the piezoelectric device deflects along the transverse direction when a voltage is applied to the electrode pairs. The driving voltage, furthermore, includes two channel control signals that driving the two symmetric parts, respectively. The two channel control signals are wherein they are two opposing phase AC control signals added to the same positive DC bias that has the same direction as the poling vectors of said symmetric parts, in that the two channel signals have a common ground terminal which is connected to the electrode that is affixed to the suspension by conducting adhesive, while the other two terminals of the driving voltage are connected to the top electrodes of the two symmetric parts. The driving voltage make half of these parts expand by d31 action while the other half, i.e., their symmetric part contract. This will result in a bending motion of the actuator along the direction of its width.
The preferred actuator is actually a split electrode in-plane bending piezoelectric actuator. Analogous to the term xe2x80x9cbimorphxe2x80x9d, it can be defined as xe2x80x9csplit-morphxe2x80x9d.
In accordance with another aspect of the present invention, a disk drive suspension having a load beam that includes a mounting region at a proximal end, a flexure and a slider at a distal end, a rigid region adjacent to a distal end and a spring region between the mounting region and the rigid region is provided. The suspension is wherein it includes slits and slots on the load beam that separate the load beam into a stationary proximal section and moveable distal section, in that each side of the load beam has at least two slits with a slot formed therebetween, and in that the slots extend from different sides of the load beam to join at the center line of the load beam and form a hinge there around which the moveable distal section can pivot. The respective at least two slits and the slot therebetween of the two sides of the load beam form at least two C shape resilient ears coupling the moving section to the stationary section and also it allows the moving section to pivot around the hinge easily.
In a preferred embodiment, a head gimbal assembly includes a piezoelectric actuator of the present invention mounted on a suspension of the present invention to connect the moveable distal section and the stationary proximal section. Furthermore, one of the two longitudinally spaced ends of the actuator is affixed to the stationary section by conducting adhesive or other known means, while another end is affixed to the moveable section. In response to tracking control voltage signals, the microactuator deflects the moving section along a tracking axis with respect to the hinge.
An advantage and novel aspect of the actuator of the present invention is its simple plate like integral structure and the concept of split electrode which enable the actuator to have a small height or thickness and large width, to have two or more parts that are electrically divided by respective pairs of electrodes, and to generate lateral displacement within the electrode plane. With these advantages and features, the actuator can be installed on the load beam of the suspension to position the read/write head to track the runout fast and accurately.
Other objects, as well as the structure and features of the present invention to achieve those objects, will be understood by considering the following detailed description of a preferred embodiment, presented with reference to the accompanying drawings.